The ‘riot’ that swept Oakwood Prison’s Cedar Wing was sparked by Welsh and Cockney criminals, furious over the distance friends and family have to travel for visits, inmates claim.

The Sunday night trouble involved up to 20 prisoners and was quelled by scores of officers, including members of the crack Tornado Squad, an elite police group.

The violence followed two rooftop protests at privately-run Oakwood, which opened only last April. It was savaged in a recent HM Inspectorate of Prisons report which said drugs were easier to get hold of than soap at the prison.

One inmate described to a relative in a phonecall that the riot was “inevitable” and warned of further violence by lags, who have dubbed the G4S-run jail “Jokewood”.

“They have totally trashed Cedar Wing, smashed the place to bits. They were shouting and pulling stuff off walls for hours. And we’re talking hardcore [prisoners].

“It was lock-down. We didn’t even get breakfast on Monday.”

The lag claimed emotions boiled over following simmering tension among prisoners whose loved ones live many miles away. The Mail understands Welsh inmates recently staged a recent rooftop demo to make their feelings known.

“It’s the Welsh and London boys,” he added, “because they are far away and can’t get the visits. If your family is travelling from Cardiff, it’s going to cost a packet. It ain’t going to happen.”

A G4S spokesman said: “The incident was brought under control just after 2am without injury to any prison officers, although one prisoner has been treated for minor injuries.

“The safety of our personnel and those prisoners in our care is our top priority, and we are grateful to our colleagues who were able to help us bring the incident to a close safely and effectively. Established incident procedures were followed correctly and worked as they were meant to.

“As an investigation has now commenced into the reasons for this disruption, as well as a criminal investigation, it would be inappropriate to comment further at this time.”

Meanwhile, a lawyer has called on the government to terminate the G4S Oakwood contract. Iqbal Singh Kang, of Gurney Harden Solicitors, said: “There is clear and irrefutable evidence that G4S are not able to run the country’s largest prison and they are not therefore competently able to discharge their contractual obligations.”